Finding time to work out in our harried lives can be one of the greatest barriers to making exercise a habit.

As an attorney logging 60-hour weeks in downtown Minneapolis, Amy Baumgarten knows this well. Recently, she noticed a busy friend’s cut biceps and asked her how she does it. The friend’s secret: intense exercise in as little time as possible.

This fitness regimen is based on an ever-evolving theory that says performing ultra-short, high-intensity workouts — sometimes as quick as four minutes a day — produces the same health benefits as longer bouts of exercise at a moderate pace. Think: swimming laps for several minutes at 90 percent of your maximum heart rate without stopping.

These minimalist exercises, as they’re called, are a part of the all-intensity programs popularized by the CrossFit-style gyms dotting the Twin Cities and the bestselling at-home DVD workouts like P90X and Insanity.

But skepticism abounds, as some doctors say the idea sounds too good to be true. The pace might be too much.

“This is working out at a level of exercise where your eyes are rolled back, or like you’re running away from a pack of rabid wolves,” said Dr. Tom Kottke, a cardiologist with HealthPartners.

Yet other health experts see a benefit in these short bursts of exercise — if applied correctly.

“There’s good reason to include it in your workouts,” said Mark Blegen, head of the Department of Nutrition and Exercise Sciences at St. Catherine University in St. Paul.

Rise of the 7-minute workout

For years, U.S. government guidelines have recommended at least 150 minutes of moderate exercise per week for good health. Those guidelines are based on multiple, large studies showing that people who exercise for 150 minutes a week tend to live longer and are less likely to develop heart disease and diabetes.

Newer research suggests otherwise. Notably, in 2006 researchers at McMaster University in Canada studied participants pedaling on stationary bikes for three minutes, alternating between 30 seconds of pedaling as hard as they could and resting briefly. Researchers found that shorter, harder workouts produced the same health benefits as 90- to 120-minute bike rides at a slower pace.

Using findings from that and subsequent studies on high-intensity interval training (HIIT), the American College of Sports Medicine (ACSM) recently came out with a total body workout that requires just 7 minutes to complete. The fitness market is now flooded with abridged workouts that promise results without having to devote hours to the gym.

Blegen went from skeptic to believer after seeing the amount and quality of studies coming out on high-intensity interval training.

“You’re talking to a guy who forever has done 60 to 90 minutes of cardio. If I can cut that down — great!”

Blegen works out several days a week, and at least one of those days he gets on a stationary bike and pedals all out for 30 seconds, then rests, then repeats the sequence 10 times.

“There’s not much room to debate that it will improve your [stamina],” Blegen said, adding that short but intense workouts also improve classic health markers, such as blood pressure, cholesterol and blood sugar levels.

What are you burning?

This type of workout isn’t for everybody, Kottke cautioned. The intensity required for the ACSM’s 7-minute workout, for instance, is too much for most people. If weight loss is your goal, longer workouts at a lower intensity are far more effective at burning fat, Kottke said. “[With] this kind of stuff, all you are doing is burning off your glycogen,” he said, referring to stored glucose or carbohydrates.

Blegen agreed the minimalist approach has its limits. He thinks it would be a mistake to scrap the more traditional, longer cardio workout from your regimen. Instead, Blegen suggests incorporating HIIT into your weekly routine.

Since hearing about HIIT from her friend, Baumgarten has been going to Discover Strength gym in Minneapolis. In between her time in the courtroom, she’s able to squeeze in a quick fitness program. But instead of doing several short workouts over the course of the week, she packs it all into 30 minutes — but only once a week. Her trainer pushes her though a series of intense strength exercises that work her legs and upper body.